The semiconductor industry has seen tremendous advances in technology in recent years that have permitted dramatic increases in circuit density and complexity, and equally dramatic decreases in power consumption and package sizes. Present semiconductor technology now permits single-chip microprocessors with many millions of transistors, operating at speeds of tens (or even hundreds) of MIPS (millions of instructions per second), to be packaged in relatively small, air-cooled semiconductor device packages. A direct by-product of higher density circuits with smaller feature sizes is smaller die and, therefore, a higher number of die formed on a wafer. Typically, a number of identical electronic devices are formed on a single wafer. In some instances, up to several thousand identical devices are formed on a wafer. More commonly, 200 to 300 identical devices are formed on a wafer. Once formed, each of the devices is electrically tested and sorted. Next, the wafer is sliced and diced to produce individual wafer portions known as die or chips. Each die or chip contains an individual device, such as an integrated circuit, a microprocessor, or other electronic device. Each die also includes leads, such as pins or balls, which are formed on the surface of the die.
In some instances, the cut lines for slicing and dicing a wafer into individual chips or die are scribed using a laser. Laser scribing is most often used on newer silicon devices incorporating fragile high performance dielectric materials. Laser scribing precedes singulation (slicing and dicing the wafer into individual chips or die) with a diamond saw. The laser scribe step removes some of the fragile materials without leaving mechanical defects in the device edge which can propagate into the active device under normal mechanical loads and cause failures. The laser scribe step also prevents long, thin, fragments of the fragile dielectric and embedded Cu metal traces from peeling up and becoming entangled in the interconnect bumps.
Currently, multiple parallel scribe lines are needed to remove material which is wider than the kerf of the diamond saw blade. Currently, the multiple parallel scribe lines are placed next to one another. For example, a first scribe line is made and then a second scribe line is made adjacent to the first scribe line. A third scribe line is made adjacent to the second scribe line. Laser scribing also produces a plume of suspended material that results from the laser ablation of the surface when the laser pulses the surface of the wafer. When the laser scribe lines are always placed one next to the other to scribe the wafer, the plume associated with the laser scribing process seems to be directed to one side of the scribe line. Portions of the plume can settle or deposit on the solder associated with the leads to the circuitry within the die or chip. In some instances, the plume may even result in opens being found as a result of plume deposits on the leads preventing electrical connection to the leads. The silicon debris from the laser scribe plume that interferes with electrical interconnection between the die and a package results in yield losses and also potentially increases the reliability failure rate.
In addition, laser scribing also takes time. Currently, continuous laser scribe lines are formed. Lasers pulse so a continuous line is actually formed by overlapping individual pulses from the laser used to scribe the wafer. The amount of overlap between pulses may be as much as 90%. Each subsequent laser pulse typically overlaps the previous pulse by 20-90%.
The description set out herein illustrates the various embodiments of the invention, and such description is not intended to be construed as limiting in any manner.